1. Field of the Invention
The present invention relates to a light intensity distribution measuring method for measuring the light intensity of a laser beam emitted by a semiconductor and to a light intensity distribution measuring device.
2. Description of the Related Art
To configure laser optical systems such as fiber optical systems and optical head devices which reproduce and record the information with respect to optical recording media such as CDs and DVDs, it is necessary that a light intensity distribution is formed in the 2D directions of a laser beam emitted by a semiconductor laser to calculate the efficiency in usage of the light and to calculate the size of the spot at the vicinity of the focusing point when the beam is focused by the optical system. Note that, to obtain the light intensity distribution of the laser beam flux in the 2D directions, it is necessary that the light intensities are measured at a plurality of locations in the beam and the measurement results are applied to a predetermined probability density function to calculate the light intensity distribution.
Therefore, as illustrated in FIG. 1, in a light intensity distribution measuring device for calculating the light intensity distribution of a laser beam flux in the 2D directions, a light intensity detector 12 which measures the light intensities at a plurality of locations in the laser beam emitted by a semiconductor laser 11, and a data processing device 13 which calculates the light intensity distribution based on the measurement results of the light intensity detector 12 are provided. The light intensity detector 12 has a photo detector 121 that converts the detected light intensities into electrical signals and a light shielding plate 122 having pin holes or slits that enable the photo detector 121 to detect a portion of the laser beam; when the light intensity detector 12 is rotated about the light emitting point of the semiconductor laser 11, the intensity of the laser beam which radiates at any given angle from the light emitting point can be detected.
Assuming that the laser beam obeys Gaussian distribution (normal distribution) shown in Equation (1) below, the data processing device 13 calculates the light intensity distribution by applying the measurement results obtained by the light intensity detector 12 to Gaussian distribution.
                    y        =                              f            ⁡                          (                                                χ                  |                  μ                                ,                σ                            )                                =                                    1                              σ                ⁢                                                      2                    ⁢                    π                                                                        ⁢                          ⅇ                                                -                                                            (                                              χ                        -                        μ                                            )                                        2                                                                    2                  ⁢                                      σ                    2                                                                                                          Equation        ⁢                                  ⁢                  (          1          )                    
Here, as shown in Equation (2) below, the light intensity distribution is expressed by the maximum intensity in the vicinity of the center of the laser beam flux, its positional coordinates (δx, δy), and the angular position (//θ, ⊥θ) of Full Width Half Maximum (FWHM), which is one half of the maximum intensity when the light beam flux is angled from the position of the maximum intensity in the X and Y directions.
                              f          ⁡                      (                          x              ,              y                        )                          =                              c                                                            -                  2                                ·                                                      (                                          x                      -                                              δ                        x                                                              )                                    2                                                                              (                                      1.6986                    ·                    0.5                    ·                                          FWHIM                      x                                                        )                                2                                              ·                      c                                                            -                  2                                ·                                                      (                                          y                      -                                              δ                        y                                                              )                                    2                                                                              (                                      1.6986                    ·                    0.5                    ·                                          FWHIM                      y                                                        )                                2                                                                        Equation        ⁢                                  ⁢                  (          2          )                    
However, when the light intensity distribution, obtained under assumption that the intensity distribution of the laser beam obeys Gaussian distribution, is compared with the actual measurement values, errors of several percentage points occur in the skirt of the intensity distribution as shown in FIG. 3. Therefore, the efficiency in usage of the laser beam or the spot size cannot be obtained accurately.